1. Field of the Invention
The present invention relates to a device and process for oscillation insulation in a transmission path having a first body that performs an oscillation movement, a second body that is connected to the first body via at least one rigid connection element, an actuator device that is arranged on the at least one connection element, a sensor unit, and a regulator unit. The invention is used for oscillation reduction or vibration reduction in helicopters.
2. Discussion of Background Information
The problem of the transmission of oscillation movements of a vibrating body to a second body connected thereto via a rigid connection element occurs in technology wherever machine vibrations and machine oscillations are generated by a source. The transmission of these oscillations and vibrations (usually called structure-borne noise) to elements rigidly connected to the source is hereby very disturbing in general.
As is known, in helicopters the main transmission gear is connected via several support structures, the so-called struts, to the upper side of the cell structure of a cockpit. This support structure or the strut are to be considered in a generalized manner as a connection element. This is thereby a rigid connection element. This connection element represents a transmission path. The main transmission gear and engine, rotor and auxiliary units generate vibrations that are passed into the cell structure of the cockpit via the struts. The disturbing high-frequency gearing vibrations are the determining factor for noise disturbance and arise through gear tooth engagement. A gearing has several pairs of gear wheels, the engagement of which leads to marked oscillations and the associated noise peaks at discrete frequencies in the range of approx. 500-4000 Hz. These noise peaks often exceed the background noise in the helicopter by 10-20 dB (FIG. 1) and thus also dominate the overall noise level. In addition, discrete frequencies are experienced as very disturbing, even if the noise level is otherwise at a low level. Further i.a. discrete frequencies are generated by the engine, the rotor and auxiliary units and likewise passed into the cabin via the gearing struts. The overall noise level (integrated over the entire frequency range) in a conventional standard helicopter is between 85-90 dBA. The gearing-induced vibrations are thus the main cause of serious noise disturbance in the cockpit.
Various arrangements and systems have been proposed to reduce this noise disturbance. U.S. Pat. No. 6,105,900 and U.S. Pat. No. 6,138,947, for example, describe an active noise control system that minimizes the undesirable acoustic noise in a helicopter cockpit. This noise is caused to a great extent by vibrations of the main transmission gear that is connected to the cell structure of the cockpit. The main transmission gear is connected to the cell structure of the cockpit by means of individual attachment feet. The individual attachment foot features a flange in the area of the interface between attachment foot and cell structure. An oscillation actuator for generating mechanical oscillations is in turn arranged on this flange. The oscillation actuator generates oscillations through the movement of an inertial mass, which oscillations are passed into the struts from the actuator via the flange and superimposed on the oscillations generated by the main transmission gear, so that a marked reduction of the resulting oscillation ensues from a superimposition of both oscillations. As a result, the noise is reduced in the cockpit of the helicopter. The known noise control system is thus based on a counter-control principle. The oscillations first introduced are detected and compensated for by means of a corresponding counter-vibration through destructive interference. However, this means that in any case undesirable forces are first introduced into the cockpit which forces are then compensated again through the targeted introduction of corresponding counter-forces that are fed in via an intake surface of the flange acting virtually in a selective manner. The known noise control system thus has the disadvantage that in any case the support structure (strut) and the cell structure of the cockpit are acted on with forces. Furthermore, the relatively high weight of the oscillation actuators is disadvantageous. It is also disadvantageous that several flanges are necessary on one support structure.
U.S. Pat. No. 6,224,014 B1 describes the reduction of noise that occurs in the helicopter due to various vibration sources (gearing, engine, rotor). The actuators are oscillation actuators that have an inertial mass to be moved. The vibration force generated by the oscillation actuator is destructively superimposed on the disturbing oscillation and not insulated from the cell structure.
European Patent Application No. EP 0 774 411 takes into consideration purely the reduction of vibration and not the reduction of noise in the cockpit which is caused by the higher-frequency oscillations of the main transmission gear. The known document considers oscillations that occur through the rotating main rotor (column 9, line 39 ff). These oscillations lie at fairly low frequencies (approx. 20-30 Hz) and are therefore not relevant in terms of noise.
Furthermore, German Patent Application No. DE 198 13 959 A1 discloses a device for suppressing structure-borne noise that reduces the transmission of machine vibrations and machine oscillations through a support structure to a cell or a component with the simplest possible construction and with relatively low integration costs. There, too, the cell or the component is, e.g., the cockpit of a helicopter. DE 198 13 959 A1 teaches that the device for structure-borne noise suppression contains at least one piezo actuator that introduces oscillations into the support structure in order essentially to block the structure-borne noise transmission path to the structure to be insulated and to compensate for the noise excitation more effectively by means of the available and excited system dimensions of the noise generator. The piezo actuator installed on the support structure thereby effects a force introduction over a relatively large surface area of the support structure. The support structure can be arranged, e.g., between the main transmission gear of a rotor and a cell structure of the cockpit of a helicopter. In this case the support structure is embodied as one or more gearing struts. The piezo actuator is arranged essentially along the entire circumference of the strut and has a defined extension in the axial direction of the strut.
However, German Patent Application No. DE 198 13 959 A1 does not provide any information on how such a device for suppressing structure-borne noise can be effectively used in an overall system or on how the regulation and control occur, taking into consideration the interaction of the individual parts and components in an overall system.